1. Field of the Invention
The present invention relates to a test system used to align the boresite of a radar antenna. More particularly, the present invention relates to a test system that is used to align the boresite of an automotive radar system antenna with a mechanical reference line (e.g., the thrust vector) from a vehicle on which the radar is mounted.
2. Description of the Related Art
Recently, manufacturers have begun producing radar systems for automobiles. Such systems have been used in combination with a vehicle cruise control to form an automotive radar system. An automotive radar system transmits a signal from an antenna typically located in the grill area of an automobile. The presence of and distance to an object from the automotive radar antenna is determined from the signal reflected by the object. If an object is detected in the path of the vehicle, wheel braking or engine deceleration is applied by the automotive radar system to maintain a desired distance from the object and to prevent the vehicle from striking the object.
To assure proper performance of an automotive radar system, the device must be regularly tested. During testing, proper alignment of the automotive radar antenna boresite angle with a mechanical reference line, such as the thrust vector of the vehicle, which identifies the forward direction of travel of the vehicle must be achieved. An automotive radar antenna boresite may become misaligned due to vehicle vibrations, vehicle collisions, or other factors. The boresite angle must be properly aligned to prevent the radar system from encountering false or inaccurate readings from signals received from vehicles in adjacent lanes, and to ensure proper detection of vehicles or objects in the immediate lane.
Referring to FIG. 1, an automotive Radar Test System (RTS) includes a transponder 115 with a single antenna 110. The transponder antenna 110 is assumed to have a centerline 111 mechanically aligned to be approximately parallel to a vehicle thrust vector 190. Further, it is assumed that the transponder antenna 100 has its centerline mechanically aligned approximately with the centerline of the radar antenna 100.
Although mechanical alignment eliminates translation errors between the centerline of the receiving antenna 110 and the centerline of the radar antenna 100, the electrical boresite of radar antenna 100 can still be misaligned as illustrated by the boresite vector 195. The boresite angles formed between the boresite vector 195 and the vehicle thrust vector 190 must be set to a minimum to ensure proper operation of the radar system.
Using the system illustrated in FIG. 1, the boresite of radar antenna 100 is considered properly aligned when a signal detected by the transponder 115 is a maximum. However, the amplitude sensitivity of the transponder antenna 110 achievable using this system is undesirably low. For example, the amplitude variance is typically less than 0.5 dB per degree of boresite offset when the radar antenna has a 3 dB beam width of 7 degrees. Thus, an alignment system utilizing only a single receiving antenna in accordance with FIG. 1 is incapable of adjusting the boresite angle of an automotive radar antenna to any great precision.
In accordance with the present invention, two receiving antennas are used in an alignment system to align an automotive radar antenna boresite angle with a mechanical reference line, such as a vehicle thrust vector, using a difference signal. The system allows a radar antenna to be easily boresited to within 0.5 degrees of a mechanical reference line.
In the system, a signal is transmitted from the radar antenna to the receiving antennas placed equidistant from the centerline of the radar antenna. Signals received by the receiving antennas are provided to detectors for further processing such as the generation of amplitude plots of difference, sum*difference, or sum/difference signals for display. The boresite angle of the radar antenna is then adjusted until the amplitude of the difference, sum*difference, or sum/difference of the detected signals reaches a minimum to align the radar antenna boresite with the mechanical reference line from the vehicle.
The receiving antennas can be mounted on a test fixture on either side of the transponder and mechanically aligned prior to boresite alignment procedures so that the centerline of the transponder antenna is aligned with the centerline of the radar antenna prior to boresite adjustment. When so aligned, the centerline of the radar antenna will be approximately aligned at a midpoint between the two receiving antennas.